Telephone transmitter



TELEPHONE TmmswilTTERA Filed March 5, 1925 Side af INVENTO'R H. J. RQUNDJUNITED STAT-Es n EN FICE.

'HENRY`JOSIPH\RUND, 0F LONDON, ENGLAND, A SSIGNOR TO RADIO CORPORATIGNOF AMERICA, A CORDORATION OF DELAW'AREI.l v

TELEPHONE TRANSMITTER.

Application 1aed March 3, 1925, serial No'.

I 'I his invention relates to. telephone transmitters of themagneto-phone type'ln Which the movements of a coil suspended 1n a mag-Anetic ield and moved by the incidence of sound Waves up`on it producedifferences of potential' which are stepped up by ta trans'- formerandapplied tothe grid of a thermionic valve by which they are ampliied.

According to this invention the coily is constructed in the form of aspiral and is mounted upon an annular support formed ofl thin paper orother suitable material, the

' Weight of' the wire being equal -or substany impaired unless the paperb e heavier andA tially equal to the Weightof the support and of theadhesive by which Ithe Wire is secured to the support. f l

The resistance 'f thecoil is chosen so that the damping resistanceusually inserted in shunt across the secondary of the transformer may beomitted. e

Preferably NI employ tissue 4paper and aluminium Wire. With this paperthe spacf ing of the Wire, which4 is about No. 40,

S. W. G., should not exceed 2 mm.; other stiffer. Such an arrangementWill not'be so sensitive.

It 1s usual to glve to speech transformer a natural resonance of about1000 cyclesper second and by shunting the secondary with a resistance ofabout 250,000 ohmsfairly uniform, response lfor.

the range from 100 to 5 000 cycles can beobtained. But With anyparticular-transformer the exact value ofthe shunt resistance to obtainthe required response curve may be determined experimentally.

-the Secondary of 'a' 12,912, and in Great isritain Maren 3, 1924..

coil connected to the primary coil equivalent al resistance in shunttothe secondary will be required so that the maximum voltage may beobtained Whilst the resonance curve remains Hat.

The invention is illustrated in the accompanyino drawing, of whichFigure lis adiagram .showing the coil l of the telephone connected totheprimary "2 of a step-up transformer Whose secondary 3 is connected` tothe grid of a thermionic valve 4. y

Figures 2 -and 3 are respectively ia section and afront elevation of thetelephone.-

Refe'rringto Figures 2 and 3, 1 is the telephone coil, 5 an'aznularpaper support, and 6 and 7'are. the poles of a magneto-phone magnet orelectromagnet. Having-described my invention What I v1. In a telephoneapparatus of the magneto-phone type, an electromagnet having an annularair gap, a fiat aperiodic annular diaphragm supported therein, and aflat spiral coil secured tosaid diaphragm.

I 2. Ina telephone apparatus of the magneto-phone type, an electromagnethaving a magnetic field, anf annular diaphragm suspended within themagnetic field;- ofsaid electromagnetya flat spiralA coil and .means forsecuring said coil to said diaphragm so that the Weight of saidVdiaphragr'ri and said se'-l curing means is approximately equal to ltheWeight ofsaid coil. "i I l [3.' Ina telephonel apparatus of themagneto-phone vtype,l an electromagnet having a'magn'etic field, a flatannular paper iia phragm suspended Within the magnetic field 'of saidelectromagnet, a flatspiral aluminum Wire coil the spacing ofsaidWiremot exceeding 2 mm; and means for` securing said coil tosaddiaphragm. By making the resistance of thel telephone HENRY JOSEPHROUND.

